The present invention relates to a target holder with mechanical scanning or sweeping permitting a homogeneous implantation or a deposition on one or more targets mounted on the device, said deposition or implantation being obtained with the aid of an energy source.
Numerous applications require targets to be struck by a high energy beam or a particle flux, e.g. ion implantation on a silicon wafer used in the production of integrated circuits. Due to the fact that the beam diameter is generally much smaller than the dimensions of the target, the main problem which arises in this type of application is that of the homogeneity of the implantation.
The various systems used hitherto can be placed in two main categories, namely mechanical systems and electrical systems. In the case of mechanical systems, the targets are mounted on a support, which moves in front of a fixed beam. The support is displaced in two crossed movements, namely a slow movement and a fast movement, which is perpendicular to the slow movement. In the prior art, for the performance of the fast movement, the targets can, for example, be placed on a drum rotating about an axis perpendicular to the beam or can be mounted on a deformable support driven by two driving wheels. There is also a system in which the targets placed on the drum constantly retain the same orientation, i.e. they remain parallel to themselves and therefore perpendicular to the beam. The slow movement in the preceding cases is an alternate translation movement in a direction parallel to the rotation axis.
The main disadvantage of such devices is that the movements are slow and the risk of implantation inhomogeneity is great, due to the variations of the intensity of the beam due to the reciprocating movements superimposed on the rotary movement. In addition, the movements of the target can be such that the orientation of the latter with respect to the beam is variable and the angle of incidence is not the same at all points of the target. Although such defects are of little importance when the plates are of small size, they become prohibitive when the size thereof increases, because the impact conditions can vary significantly from one point to another.
Another category of devices uses plates on which are mounted the targets, the rotary axis of the plate being parallel to the beam. The fast movement is in this case rotation, whilst the slow movement is performed by a displacement, parallel to itself, of the rotation axis of the plate, in a plane passing through the beam axis. This device has the advantage that the angle of incidence of the beam on the target is constant. However, it has the disadvantage that the radius of the trajectory of the beam on the target is variable. The lines are not parallel and although the rotation speed is constant, the relative linear velocity of the beam and the target is variable and is dependent on the distance between the beam and the rotation axis. This makes it necessary to have negative feedback systems on the slow speed, in order to obtain a good homogeneity on the target.
In electrical systems, the targets are fixed, but scanning is effected by varying the direction of the ion beam. In view of the fact that the deflection angles increase with the size of the plates, this leads to implantation inhomogeneities despite electronic corrections made during the scanning time.